NEW YORK (Reuters Health) - In elderly people, higher levels of calcium in the blood are associated with poorer mental function and faster decline in cognitive ability, Dutch researchers have shown.

Some diseases that increase blood calcium -- such as kidney failure, cancer and excessive parathyroid gland activity -- could be a factor in the relationship, although it's also possible that an individual's calcium "set point" plays a role in cognitive decline with age, note Dr. Miranda D. Schram and colleagues in the Journal of the American Geriatrics Society.

Several studies have shown that small but long-term elevations of calcium within nerves and brain cells can kill them, Schram of Leiden University Medical Center and her team point out. Calcium can pass from the blood stream into the brain, they add, but it has not been clear whether blood calcium levels have any relationship to cognitive function.

To investigate, the researchers analyzed results of the Rotterdam study, in which nearly 8,000 people 75 and older were followed for about 11 years, and the Leiden study, which included almost 600 men and women aged 85 who were followed until they were 90.

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In both groups, Schram and her team found, higher blood calcium was related to worse cognitive function at the study's outset as measured by a test known as the Mini-Mental State Examination. Poorer memory and executive function also were associated with higher calcium levels.

Higher calcium levels were also tied to faster mental decline over time in the Rotterdam study, but not in the more elderly group in the Leiden study.

When the researchers excluded people with abnormally high calcium levels from their analysis, the link between calcium levels and cognitive function was actually strengthened.

More study is needed, the researchers conclude, to understand the mechanisms by which calcium levels both within and outside nerve cells might contribute to mental decline.